Internal combustion engines frequently employ fuel delivery systems in which fuel is delivered to the engine with at least one fuel injector. This fuel system generally includes a fuel source and a high pressure pump which delivers fuel to each injector through a supply line. Where the engine has multiple fuel injectors, each fuel injector is often coupled to a fuel rail, the injectors spaced along the length of the rail. The high pressure pump delivers fuel under pressure to the rail, and thus the injectors.
Each injector includes a nozzle through which fuel passes into an air stream (such as in an intake pipe or passage) or directly into a combustion chamber of the engine. The injector may be solenoid operated, such that upon activation, fuel under pressure in the rail passes into the injector and out its nozzle. When not activated, fuel is prevented from passing through the injector. In this manner, the flow of fuel to the engine is controlled.
Fuel which is delivered to the fuel rail but not supplied to the engine by the injector(s) is preferably routed back to the fuel supply for re-delivery. This fuel should be returned to the fuel supply without lowering the high pressure of the fuel within the fuel rail, this high pressure being necessary for proper atomization of the fuel delivered by each injector. Thus, a pressure regulator is positioned at the end of the fuel rail between the injectors and a return line.
FIG. 1 illustrates such a prior art fuel return arrangement. As illustrated, a pressure regulator 200 is positioned at the end of a fuel rail 202. The regulator 200 has a body or housing 204 which is separated into a top chamber 206 and a bottom chamber 208 by a diaphragm 210 connected to a valve disc 212. A spring 214 presses the disc 212 downwardly over the opening of a fuel return line 214. A reference line 218 in communication with the top chamber 206 extends from the regulator 200 to a portion of the air intake system of the engine.
In operation, as the pressure within the fuel rail 202 increases, it eventually overcomes the pressure of the air within the top chamber 206 and that force applied by the spring 214, and moves the diaphragm 210 upwardly. As this occurs, the disc 212 moves off of the opening of the return line 216, and fuel flows back to the fuel supply.
As can be appreciated, when the engine is operating at high speeds, the pressure regulator works efficiently. When the engine speed is high, a high pressure within the top chamber 206 combines with the force supplied by the spring 214. Thus, before the return line 216 is opened, a very high pressure in the fuel rail 202 must be achieved. In this manner, the pressure within the fuel rail 202 remains high. The high pressure fuel within the rail 202 which is delivered through the injectors is well atomized as it passes through the nozzle thereof.
At low engine speeds or loads, however, the air pressure within the top chamber is low, and the fuel pressure in the fuel rail may be relatively low and still raise the disc 212, permitting fuel return. Thus, the fuel pressure in the rail remains low, and the fuel is not well atomized. In addition, the engine operating temperature is low. Some of the fuel delivered into the combustion chamber hits the cylinder walls, cylinder head or other engine components and is vaporized. On the other hand, because the engine temperature is low, other of the fuel (which is not well atomized because the fuel pressure is low) is not vaporized. The result is unstable or incomplete combustion because of the large differences in the air/fuel mixture throughout the combustion chamber, lending to engine inefficiency and low power.
It is desired to provide a fuel supply system which includes a fuel return, but which also provides fuel to the engine in a manner which promotes stable combustion across the entire operating range of the engine.